MRK, Daiichi Begin Phase III Breast Cancer Study With ADC Candidate

Group 1: Study Initiation and Objectives - Merck and Daiichi Sankyo have initiated the phase III HERTHENA-Breast04 study to evaluate the investigational HER3-directed ADC, patritumab deruxtecan (HER3-DXd), for treating specific breast cancer patients [1][2] - The study will compare HER3-DXd against an investigator's choice of treatment in patients with unresectable locally advanced or metastatic hormone receptor positive, HER2 negative breast cancer who have progressed after endocrine and CDK4/6 inhibitor therapy [2] - The primary endpoints of the study include progression-free survival and overall survival, while secondary endpoints encompass objective response rate, duration of response, and safety [3] Group 2: Clinical Development and Collaboration - The HERTHENA-Breast04 study is based on promising data from previous studies, including ICARUS-Breast01, where HER3-DXd showed positive responses in metastatic breast cancer patients [3] - Merck has acquired global co-development and co-commercialization rights to two additional ADCs from Daiichi Sankyo for a total potential consideration of up to $22 billion, although Daiichi retains exclusive rights for development in Japan [10] - Merck has also expanded its collaboration with Daiichi to co-develop MK-6070, an investigational T-cell engager targeting DLL3, obtained from Harpoon Therapeutics [11] Group 3: ADC Market and Competition - ADCs are viewed as a disruptive innovation in the pharmaceutical industry, enhancing cancer treatment by using antibodies to deliver cytotoxic drugs directly to tumors [13] - Daiichi Sankyo is actively developing several ADCs across various cancer types, including Enhertu, which is marketed in partnership with AstraZeneca and approved for multiple indications [14] - Pfizer has entered the ADC market through the acquisition of Seagen for $43 billion, adding three ADCs to its portfolio that have significantly contributed to its revenues [15][16]